If you don't have half shafts and a driveshaft yet the half shafts at minimum would be a good idea especially if you drag race the car. The 18s snap half shafts easily. We snapped our drivers side one on the stock calibration with just a set of drag radials.
As for more power at this point it's either nitrous or forced induction. Plenty of options available here with custom tuning from the best in the industry.